Contrary to the term "vault" being used in this thread, most casinos do not have a "vault" in the casino cage. In fact I've never seen one that did. I don't doubt that its possible, some do.

Every chip, bill, check, wire transfer (either way), coin, TITO, credit, deposit, etc in the cage must be counted 3 times a day at shift change. Some casino cages might handle more tranactions a day than most banks do.

What a cage has is a lot of cabinets.
Some will be designated "Double Custody, meaning, the key is kept at the security podium. Key personnel in the cage are designated to sign for it. When they do, a security guard will return with them to the DC cabinet and watch while they add or remove chips. Both then return and sign the key back in.

DC cabinets allow the cage to store extra or reserve chips. A tape is run for all chips in it and posted on the locked cabinet. This allows the count to be credited for the total in the cabinet from the tape, without counting them 3 times a day. DC cabinets can go for months with the same total.

If any of you have ever seen the Palms chip displays at our cage, it is an example of a DC cabinet. Only one cage S/M or I, can sign for it. A security guard accompanys us when we add chips.
It always takes two signatures to get a DC key. Security must be one.

When we buy $1 chips we normally order 40,000, might only need 10,000 in the fill bank. 30,000 are put in DC.

When a casino changes chips and do not want to destroy the old rack, it goes in DC. Thats why you might ask for older chips knowing they have them, but the cashier says we don't have them. She has no idea whats in DC. If she does know, its more trouble to get them for you than its worth.